Electrical Overstress – 2 Exercises TI Precision Labs – Op Amps

1. For the circuit below: simulate the response to this pulse. Will the 30V pulse cause EOS damage?

+15V

-15V

+15V

-15V Vin

R2 100

C1

1n

+VG1

+

VG2

Vpulse

Vout

Rf 20kR1 1k

-

+ +U2 OPA171

V1 15

V2 15

Time (s)0 50n 100n

Vpulse

0.00

30.00

10ns pulse

3

2. For the circuit below: simulate the response to this pulse. Will the ±5V square wave cause EOS damage? Draw the differential input waveform, the output waveform, and input current waveform.

Electrical Overstress – 2 Solutions TI Precision Labs – Op Amps

5

1.! For the circuit below: simulate the response to this pulse. Will the 30V pulse cause EOS damage?

No. The RC circuit keeps the pulse from reaching overstress levels on the input. RC = 100ns and the pulse is only 10ns.

+15V

-15V

Vin

R2 100

C1

1n

+

VG1

+

VG2

Vpulse

Vout

Rf 20kR1 1k

-

+ +U2 OPA171

T

Time (s)0 50n 100n

Vin

0.00

2.86

Vout

-5.12m

74.98m

Vpulse

0.00

30.00

10ns pulse

6

2.! For the circuit below: simulate the response to this pulse. Will the ±5V square wave cause EOS damage?

Yes. The current flowing into the input is greater than 10mA (about 65mA). This exceeds the absolute maximum input current limit. Increasing the 10! series resistance could help protect the amp.

When the input transitions from +5V to -5V the output cannot instantaneously transition. Thus the potental difference between the input and output is 10V. Most of the 10V is across the 10! input resistance. This causes a very high current to flow, limited by the op amps short circuit limit (65mA in this case). I_input_max = (10 – 0.7)/10! = 430mA (beyond op amp short circuit limit) I_input_expected " 65mA from short circuit limit

7

2. For the circuit below: simulate the response to this pulse. Draw the differential input waveform, the output waveform, and input current waveform. Note that the input current is limited by the short circuit limit of the amplifier and is above the absolute maximum of the amplifier.